1. Field of the Invention
This invention relates to new and useful improvements in pumpdown pistons or impeller units used in pumpdown or through the flowline (TFL) operating systems. This invention may also be used on a well swab. The servicing of oil and gas wells by pumpdown or through the flowline (TFL) techniques has become more common as the number of offshore installations having satellite wells connected by flowlines to a central facility has increased. In some offshore installations, the well servicing equipment may have to travel as much as twenty miles through a flowline connecting the production platform to the underwater wellhead.
2. Description of the Prior Art
Many modifications have been developed for pumpdown pistons to reduce wear when the seal units rub against the interior surface of a flow conductor.
U.S. Pat. No. 4,078,810 to H. P. Arendt discloses a piston type seal unit having an annular choke ring. A predetermined value of differential pressure across the fins is used to expand the choke ring and thus reduce seal unit wear. U.S. Pat. No. 4,078,810 contains an excellent discussion of the working environment and design considerations in selecting a pumpdown or TFL piston.
U.S. Pat. No. 3,957,119 to J. H. Yonker shows a conventional pumpdown piston. U.S. Pat. No. 3,543,852 to Donald F. Taylor discloses a pumpdown piston having an internal bypass structure to limit the differential pressure across the seal units. U.S. Pat. No. 3,543,852 also discusses the construction of fins or lips on the seal unit to allow bypass flow around the exterior of the piston to limit the differential pressure across the seal unit.